FIGURE 4.11 Layout of Fujitsu hydraulic pulse motor-stepmotor combination with a hydraulicservomotor, a) General view of the device; b) Leftward movement of the valve's piston; c) Crosssection of the oil distributor............................................................................................................35

FIGURE 4.18 Comparison between the experimental (solid line) and the calculated (dashed line)speed of the cam of the one-revolution mechanism during operation............................................40

FIGURE 7.11 Active orientation of a flat, square part: a) Turning in the plane of the part; b)Turning over to the second side......................................................................................................66

FIGURE 7.12 Active orientation of cylindrical details due to the difference between the center ofmass and the geometric center........................................................................................................66

"Pick and place robot—A simple robot, often with only twoor three degrees of

freedom, which transfers items from place to place by means of point-to-pointmoves.

Little or no trajectory control is available. Often referred to as a 'bangbang' robot."

"Manipulator—A mechanism, usually consisting of a series of segments, jointed or

slidingrelative to one another, for the purpose of grasping and moving objects usually

in several degreesof freedom. It may be remotely controlled by a computer or by a

human." [Note: The words"remotely controlled.. .by a human" indicate that this device

is not automatic.]

"Intelligentrobot—Arobot which can be programmed to make performance choices

contingent on sensoryinputs."

"Fixed-stop robot—A robot with stop point control but no trajectory control. That

is,each of its axes has a fixed limit at each end of its stroke and cannot stop except at

one or theother of these limits. Such a robot with AT degrees of freedom can therefore

FIGURE

1.2

Manipulator or

automatic arm.

stop at no more than2N

locations (where location includes position and orientation).

Somecontrollers do offer the capability of program selection of one of several mechanical

stops to beused. Often very good repeatability can be obtained with a fixed-stop

robot."

"Android—A robot which resembles a human in physical appearance."

"Sensory-controlled robot—A robot whose program sequence can be modified as a

function ofinformation sensed from its environment. Robot can be servoed or nonservoed.

(See Intelligentrobot.)"

"Open-loop robot—A robot which incorporates no feedback, i.e., no means of comparing

actual output to command input of position or rate."

"Mobile robot—A robot mounted on a movable platform."

"Limited-degree-of-freedom robot—A robot able to position and orient its end effector

in fewerthan six degrees of freedom."

We will not discuss here the problem of the possibility (or impossibility) of actually

creating arobot with a "human soul." The subject of our discussion will be limited

mainly to industrialrobots, including those

which belong to the family of bangbang

robots. The application of theserobots in the modern world must meet the requirements

of industry, including functional andmanufacturing demands and economic

interests. Obviously, esthetics and environmentalconsiderations are also involved. The

mechanical component of the design of robotic systemsconstitutes the main focus of

our consideration.

1.2

Definition of Levels or Kinds of Robots

Every tool or instrument that is used by people can be described in a general form, as is shown inFIGURE

1.3. Here, an energy source, a control unit, and the tool itself are connected in someway. The three components need not be similar in nature or in level of complexity. In thissection, when examining any system in terms of this scheme, we will decide whether it belongsto the robot family, and if so, then to which branch

FIGURE

1.3

Energy-control-tool relations.

of the family. It is easyto see that this scheme can describe any tool: a hammer, a spade, anaircraft, a computer, a missile, a lunar vehicle, or a razor. Each of these examples has an energysource, a means of control, and the tools for carrying out the required functions. At this stage weshould remember that there is no limit to the number of elements in any system; i.e., a system canconsist of a number of similar or different energy sources, like or unlike means of control fordifferent parameters, and, of course, similar ordifferent tools.

FIGURE

1.4

Classification of tools used in industry.

The specific details of this kind of scheme determine whether a given system can be defined as arobot or not. Let us now look atFIGURE

1.4

(examples I to X) which shows the variouspossibilities schematically.

1. The energy source is a person, and his or her hands are the means of control; for example, ahammer, a shovel, a spade, a knife, or

a sculptor's chisel. Indeed, when a person manipulates ahammer, the trajectory of this tool, the power of its impact, and the pace of action are controlledby the operator. In this case, the feedback or the sensors which inform the operator about the reallocation of the hammer, its speed, and its accumulated energy are the muscles of the arm, thehand, the shoulder, and the eyes. Obviously, this is also true for a spade or a chisel.

2. The energy source is a motor, but the means of control are still in human hands; for example, asimple lathe, a motor-powered drill, a dentist's drill (would anybody really be prepared to entrustthe operation of such a tool to some automatic controller?), a motor-driven sewing machine, anelectric or mechanically driven razor. To some extent, this group of machines also includesmachines driven by muscle power of another person (or animal) or even driven by the legs of thesame person.

1.3

Manipulators

Let us return here to the definition of a manipulator, as given in Section1.1. A manipulator maybe defined as "a mechanism, usually consisting of a series of segments, jointed or sliding relativeto one another, for the purpose of grasping and moving objects usually in several degrees offreedom. It may be remotely controlledby a computer or by a human". It follows from thisdefinition that a manipulator may belong to systems of type 1 or 4, as described in Section 1.2,and are therefore not on a level of complexity usually accepted for robots. We must thereforedistinguish between manually activated and automatically activated manipulators. Manuallyactivated manipulators were created to enable man to work under harmful conditions such as inradioactive, extremely hot or cold, or poisonous environments, under vacuum, or at high

pressures. The development of nuclear science and its applications led to a proliferation in thecreation of devices of this sort. One of the first such manipulators was designed by Goertz at theArgonne National Laboratory in the U.S.A. Such devices consist of two "arms," a control armand a serving arm. The connection between the arms provides the serving arm with the means ofduplicating, at a distance, the action of the control arm, and these devices are sometimes calledteleoperators. (Such a device is a manually, remotely controlled manipulator.) This setup isshown schematically inFIGURE

1.5, in which the partition protects the operator sitting on themanual side of the device from the harmful environment of

the working zone. The serving arm inthe working zone duplicates the manual movements of the operator using the gripper on his sideof the wall. The window allows the operator to follow the processes in the working zone. Thismanipulator has seven degrees

of freedom, namely, rotation around theX-Xaxis, rotation aroundthe jointsA,translational motion along the F-Faxis, rotation around the F-Faxis, rotation aroundthe jointsB,rotation around the Z-Zaxis, and opening and closing of the grippers. The kinematicsof such a device is cumbersome and is usually based on a combination of pulleys and cables (orropes). InFIGURE

1.6

we show one way of transmitting the motion for only three (out of thetotal of seven) degrees of freedom. The rotation relative to theX-X axisis achieved by thecylindrical pipe 1 which is placed in an immovable drum mounted in the partition. The length ofthe pipe determines the distance between the operator and the servo-actuator. The inside of thepipe serves as a means of communication for exploiting the other degrees of freedom. Therotation around the jointsA-Ais effected by a connecting rod 2 which creates a four-bar linkage,thus providing parallel movement of the arms. The movement along thisY-Yaxis is realized by asystem of pulleys and cable 3, so that by pulling the body 4, say, downwards, we causemovement of the

FIGURE

1.5

Manually actuated manipulator/teleoperator.

body5in the same direction. This is a result of the fastening of the bodies 4 and 5 to thecorresponding branches of the cable 3. By adding more pulleys and cables, we can realizeadditional degrees of freedom. Obviously, other kinematic means can be used for this purpose,including electric, hydraulic, or pneumatic means. Some of these means will be discussed later.The mimicking action of the actuator arm must be as accurate as possible both for thedisplacements and for the forces the actuator develops. The device must mimic the movement ofa human arm and palm for actions such as pouring liquids into special vessels, keeping thevessels upright, and putting them in definite places.

FIGURE

1.6

Kinematic example of a threedegrees-of-freedom teleoperator.

Bothin principle and in reality the teleoperator is able to perform many other manipulations.Obviously the number of degrees of freedom attributable to a manipulator is considerably lessthan the 27 degreesof freedom of the human arm. The operator of such a device thus has to bespecially skilled at working with it. At present, engineers are nowhere near creating amanipulator with 27 degrees of freedom, which would be able to replace, at least in kinematicterms, the human arm. An additional problem is that a human arm, unlike a manipulator, issensitive to the pressure developed, and the temperature and the surface properties of the object itis gripping. To compensate for the limited possibilities of the teleoperators, the workplace and theobjects to be manipulated have to be simplified and organized in a special way. Let us now makea brief survey of automatically acting manipulators. The primary criterion used to distinguishbetween different types of manipulators is the coordinate system corresponding to the differentkinds of degrees of freedom. The simplest way of discussing this subject is to look at schematicrepresentations of some of the possible cases.FIGURE

1.7, for example, illustrates the so-calledspherical system. It is easy to imagine a sphere with a maximal radius of r1

+ r2

which is the

FIGURE

1.7

Layout of a spherical manipulator.

domain in which, inprinciple, any point inside the sphere can be reached by a gripper fixed to theend of

an arm. In reality, there are certain restrictions imposed by the real dimensions of the

linksand the restraints of the joints which result in a dead zone in the

middle of the

sphere. Sometimesthe angle of rotationФ

is also restricted (possibly because, for

instance, of the twisting of pipesor cables providing energy and a means of control to

the links).

InFIGURE

1.8

we show acylindrical manipulator. This kind of manipulator is also

called a serpentine. When the links arestraightened so that the arm reaches its maximal

lengthrl

+ r2,we can imagine a cylinder drawnby the manipulator for variablesФand

Z.This cylindrical volume delineates a space in which themanipulator can touch every

point. In reality, here as in the previous case, a dead zone appears inthe neighborhood

of the vertical axis for the same reasons mentioned above. The angle of rotation~ may

also be restricted for analogous reasons.

InFIGURE

1.9

a Cartesian-type manipulator isshown. A parallelepipedon based on

the maximal possible displacements along theX, Y,andZaxes can be imaged. Here

no rotational movements exist. Every point of the space inside theparallelepipedon

is reached by corresponding combinations of coordinates.

Combinations ofdifferent coordinate systems are often used in the design of manipulators.

InFIGURE

1.10

wesee a combination of rotational and translational movement

to provide variable valueR.Part 1can rotate around its longitudinal axis, creating an

additional degree of freedom.FIGURE

1.11

gives another example of a combination of

coordinate systems

this time a Cartesian andcylindrical manipulator. There are obviously

other possible combinations, and we will discusssome of them later on.

Let us now look at the concept of the "fracture" of a degree of freedom.For instance,

an indexing mechanism which rotates through a definite angle before stopping and

carrying out a point-to-point rotation can be denned as a half-a-degree-of-freedom

device. Themanipulators described above are driven by electric or other kinds of motors:

thus, they do notdependon human power, and the drive is able to overcome useful,

harmful and inertial resistanceto develop the required speed of action. There are,

however, problems with devices of this naturewhich do

FIGURE

1.8

Layout of a

cylindrical

manipulator.

FIGURE

1.9

Layout of a

Cartesian

manipulator.

not arise with the manuallyactivated devices described previously; namely, the control of themovements must be

organized artificially, and what would be a natural action for a manuallyoperated

by means of alever system 11 so as to impart the right pitch to the spring. The other

cam 10 controls the wirecutter 12. The layout provides the following wire-cutting

process. During a processing periodTcam 10 compresses a spring 13 on the rod of

the follower 14; when the follower 14 reaches thehighest point on the profile it jumps

down from the step. At this moment spring 13 actuates thelevers 15 and the cutter 12,

which slides along guides 16.

Note that the layout need not be kept toscale; the main point, when designing the

kinematic layout, is to include every element or link ofthe transmission and mechanism.

At this stage, too, the ratios, speeds, displacements, andsometimes accelerations must

be defined. The layout should also show every support and guide.Thus, the ratios of the

belt drive 2 (see Figure 2.17) and worm-speed reducer (3 and 4) must bespecified in the

layout. For instance, if the initial speed of the motor 1 is about 1,500 RPM andthe cycle

durationT=1.2sec, the belt drive and the reducer together must provide the ratio:

This ratio can be apportioned between the belt drive and reducer in, say, the following

way:

where the ratio of the belt drivei1

= 1.25 and that of the worm reduceri2=24.

3.

Industrial robots representation inpraxis

Industrial robots are universal automats able to make manipulation and technological operationsespecially by the production machine. Programmable in various axis and using arms, tools orsensors are able to make various work jobs.

Manipulators are man control equipment that simplify making of physically demanding job andalso manipulation equipment with lower degree of freedom. One-shot manipulators act toautomate manipulating jobs for the most of the one-shot machines in lines by massive and serialproduction. Manipulator simple motions are joined with production equipment. There is aclassification of manipulation equipment in Figure

3.1.

FIGURE

3.1

Classification of manipulation equipment according to control mean

In term of use robots can be divided to:

a)

manipulation (feeding half-finished products and components),

b)

technological (welding, assembly, paint application),

c)

special (working underwater, in universe, in radioactive environment),

d)

universal (combination of mentioned types).

The first generation robots are designed to make hardly programmed sequences of operations.

Assembled program is built-upon base of the concerning production operation to achiveverequired aim. By changing this aim it is needed to make also the program change.

The second generation industrial robots are equipped by wide range of sensors or camera view-

From the view od simulation the classification according to the type of kinematic structureisconclusive:

1.

Robots withcartesian workspace:

Kinematicstructure is created by three translation pairs,hence the denotation TTT.

The workspace (Figure 3.2) is cuboid or cube with orthogonal coordinate system.

From the view of accuracy it is the most accurate system, which can bemathematically derived. It is used mainly in large manipulation spaces.

FIGURE

3.2

Workspace of robot with cartesian coordinate system

2.

Robots with cylindric workspace:

Workspace (Figure 3.3) is a part of cylinder.System is very robust with simplecontrol.

FIGURE

3.3

Workspace of robot with cylindric coordinate system

3.

Robots with spheric workspace:

Part of sphere thatcreates robot’sworkspace is operated by arm made of two rotatingand one translating kinematic pair.

Mobility and well placed control zone isconditional by more complex control and smaller workspace

(Figure3. 4).

FIGURE

3.4

Workspace of robot with spheric coordinate system

Robots SCARA are the modification.Their kinematic structure ismade from the same parts asthe kinematic structure of robots with spheric workspace (Figure 3.5) but work operations aremade vertically.

SCARA robots work in flat cylindrical ring and

reach high speed of motion andacceleration.

FIGURE

3.5

SCARA robot scheme

4.

Robots with angular workspace:

Angular robotis

robot,which all arms make rotational movement.This robot moves in all 6 axiswith open kinematic chain.

Workspace (Figure 3.6)

is a part of space that is possible to reach byeffector. Cuts byworkspace (Figure 3.7) are usuallydelivered by producer.

Workspace is usuallybounded by cover plane.

FIGURE

3.6

Workspace of angular robot

FIGURE

3.7

Cut of angular robot workspace

At present robots with this construction are most used in praxis because their excellentmanipulation ability and high mobility helps them nicely avoid obstacles. But by more difficultcontrol achieve lower work precision.

Using ofangular robots is various and depends on the type of used tentacle. In praxis angularrobots are used to manipulate with loads, in technological operations e.g. welding

robots in pointor arc welding or thanks to theis good mobility in color application to products.

4.

Kinematics and Control of

Automatic

Machines

4.1

Camshafts

It is not always possible to satisfy the desired position function by means of the

mechanisms. Therequirements dictated by the timing

diagram (see Chapter 2) vary, but they can often be met byusing cam mechanisms.

The idea underlying such mechanisms is clear from Figure 4.1a), inwhich a disc cam

is presented schematically. A linearly moving follower has a roller to improvefriction

and contact stresses at the cam profile-follower contact joint. It is easy to see that, by

rotating the cam from positions 0 to 11, the followerwill be forced to move vertically

inaccordance with the radii of the profile. Graphical interpretation of the position

function has theform shown in Figure 4.1b). During cam rotation through the angle

Ф1

(positions 0-1-2-3-4-5) thefollower climbs to the

highest point; during the angleФ2

(6-7-8-9-10-11) it goes down, andduring the angle 03 the follower dwells (because this

angle corresponds to that part of the profilewhere the radius is constant). Changing

the profile radii and angles yields various positionfunctions, which in turn produce

different speeds and acceleration laws for the followermovements. Figure 4.2

illustrates

the cosine acceleration law of follower movement. Theanalytical description of

this law is given by the following formulas:

FIGURE

4.1

a) Disc cam mechanism; b) The follower motion law.

To provide the desired sequence and timing of actions, it is convenient to mount

all cams neededfor the machine being designed on one shaft,thus creating a camshaft,

for example, as shown inFigure 4.3. One rotation of this shaft corresponds to one

cycle of the machine, and thus onerevolution lasts one period orTseconds. As can

be seen

from Figure 4.3, a camshaft can drivesome mechanisms by means of cams

(mechanisms A, B, C, and D), some by cranks (mechanismE), and some by gears (mechanism

F). Sometimes a single straight shaft is not optimum for agiven task. Then the